OWA cannot modify all-day events

Hi,

We recently migrated successfully from Exchange 2010 to 2013.

Unfortunately now none of our employees is able to modify  all-day events in outlook web app when using Chrome (35.0.19.16.153) in Windows or Chromium (34.0.1847.116) in Linux. Also not possible in Firefox 30 in Linux.

When right-clicking an all-day event, there is just the setting "new" available.

br

guenther